1. Field of the Invention
The present invention relates to an improvement in a motor drive control device for an AC motor that is variable-speed-controlled with power supplied from a DC drive power source via a semiconductor bridge circuit, and in particular to a motor drive control device equipped with monitoring and preliminary check functions to stop the AC motor without fail, if any abnormality occurs in a drive control circuit for taking variable-speed control.
2. Description of the Related Art
A motor drive control device (hereinafter also referred to as a motor control device) is already well-known that is equipped with an additional safety stop circuit, and in which an abnormality of the safety stop circuit itself can be detected before activating the motor drive control device.
For example, “Motor controller equipped with safety shutdown circuit” described in Patent document 1 below includes a gate drive circuit that drives an inverter for inverting DC to AC in response to motor drive command from an external upper-level device; a PWM generation circuit that generates a PWM signal supplied to the gate drive circuit; and a safety stop circuit that is interposed between the gate drive circuit and PWM generation circuit; wherein the safety stop circuit includes an external motor stop switch, a plurality of three-state buffers that interrupt the PWM signal in cooperation with the motor stop switch and a monitor circuit configured such that the upper-level device can determine an abnormality of such a safety device itself.
The monitor circuit includes a logic circuit to which at least one of the output signals from the three-state buffers is input and semiconductor elements that are supplied with an output signal from the logic circuit and turned on/off based on the output signal, and the upper-level device is enabled to determine an abnormality occurring in the safety device itself based on combination of on/off states of the motor stop switch and on/off states of the output signal from the monitor circuit.
Moreover, according to “Engine air-intake control device and engine air-intake control method” described in Patent Document 2 below, the device is configured including a drive control circuit and monitor control circuit, in such a way that the drive control circuit generates conduction drive output DR2 in response to detected output from an acceleration pedal press-down sensor and air-intake valve opening degree sensor, and thereby controls a drive switching element connected to a motor for controlling the air-intake valve opening degree. The monitor control circuit stops the control operation of the drive switching element based on conduction inhibit output SP2, as well as drives a power supply interruption element provided in a motor power supply circuit based on power supply drive output DR1, and the drive control circuit is enabled to stop the operation of the power supply interruption element based on power supply inhibit output SP1.
Furthermore, when starting operation, the device can determine effectiveness of the power supply inhibit output SP1 and conduction inhibit output SP2 based on status signals ST1 and ST2, and can clear the inhibit output after normal operation is confirmed. In particular, the drive control circuit or monitor control circuit to which the foregoing status signals are supplied is configured in such a way that the circuit compares the logical states of the status signals memorized in advance for each time step with actual logical states of the status signals for each time step, and includes an operation-start-permit means that memorizes the disagreement and continues to generate the conduction inhibit output or the power supply inhibit output when the comparison results disagree with each other; when starting operation, the circuit confirms that the power supply inhibit output circuit and conduction inhibit output circuit are effectively functioning, and following that, clears each inhibit output, so that the power supply drive output and conduction drive output are made effective.
Patent Document 1: Japanese laid-open Patent Publication No. 2010-104187 (FIG. 1, Abstract)
Patent Document 2: Japanese Laid-open Patent Publication No. 2004-285856 (FIG. 6, Paragraphs [0060]-[0063], FIG. 9, Paragraph [0134])
“Motor controller equipped with safety shutdown circuit” according to Patent Document 1 as described above includes a plurality of three-state buffers connected in series between the PWM signal generator that controls conduction of switching elements for the motor and the gate circuit that controls conduction of the switching elements, and stops the motor in a safe manner by means of the three-state buffers that respond to command from a motor stop switch. The control device not only provides a stop means that does not utilize a contactor control means that interrupts power supply to the motor if any abnormality occurs, but also determines whether or not the plurality of three-state buffers are operating normally, and reports the result to the upper-level device.
However, if any abnormality occurs in the PWM signal generator itself, the problem has been that the motor control device cannot shut down the three-state buffers by detecting the abnormality. In addition, another problem has been that preliminary check cannot be conducted as to whether or not the three-state buffers properly transmit and interrupt drive command signals to six switching elements constituting a three-phase full-wave semiconductor bridge circuit.
Moreover, in the “Engine air-intake control device and engine air-intake control method” according to Patent Document 2 as described above, the switching element for interrupting power supply and the drive switching element are provided in a power supply drive circuit for the motor; the drive control circuit generates the conduction control output DR2 to the drive switching element and the power supply inhibit output SP1 to the switching element for interrupting power supply; the monitor control circuit generates the conduction inhibit output SP2 to the drive switching element and the supply drive output DR1 to the switching element for interrupting power supply; and when starting operation, the control device checks and confirms that the switching element for interrupting power supply and drive switching element are turned off without fail by the power supply inhibit output SP1 and conduction inhibit output SP2.
Therefore, the drive control circuit and monitor control circuit cooperate to detect an abnormal state of each switching element, and if any abnormality occurs, the circuits are enabled to stop the motor by turning off either one of the switching elements; however if any abnormality occurs in either the drive control circuit or monitor control circuit, there has been a problem in that all of the six switching elements constituting, for example, the three-phase full-wave semiconductor bridge circuit cannot be turned off at once.